1. Technical Field
The present invention relates to a magnetic disk drive and, in particular, to a head unlatch controlling method and arrangement in a hard disk drive employing a magnetic latch mechanism.
2. Related Art
A hard disk drive, widely used as an auxiliary memory device for a computer system, is largely divided into two parts: a printed circuit board assembly (PCBA) including most circuit components installed on a printed circuit board (PCB); and a head disk assembly (HDA) including most mechanical components, such as a head and a magnetic disk, and several circuit components.
As explained in more detail below, the typical control of a hard disk drive involves the use of a head unlatch controlling method. Such a method results in movement of the heads of the hard disk drive, which were previously parked in parking zones ofthe disks of the hard disk drive, to data areas of the disks. However, problems are experienced with such head unlatch controlling methods. In particular, a servo address mark (SAM) located in the servo sector of the disk is not accurately detected when the heads move from the parking zones. Furthermore, a read/write channel circuit typically employed in controlling the hard disk drive is not sufficiently stabilized, and this makes it impossible to accurately obtain position information relative to the heads. Accordingly, head unlatch is controlled by predetermined current and time values, and this is referred to as an "open loop" mode of operation.
The latter controlling method may be reliable under conditions of uniform and invariable performance of the parts of the hard disk drive, but problems arise when designs of the parts are frequently modified and when the modified parts exhibit non-uniform performance. In such cases, the hard disk drive may not be controlled by use of the predetermined current and time values typically employed in the open loop mode of operation.
The following patents are considered to be representative of the prior art relative to the invention, but are burdened by the disadvantages set forth herein: U.S. Pat. No. 5,144,504 to Kitazawa, entitled Method Of Controlling Positioning Of Magnetic Head Of Disk Drive Unit And Disk Drive Unit Executing Same, U.S. Pat. No. 5,241,435 to Saito et al., entitled Servo Information Recording Method For A Storage Apparatus, U.S. Pat. No. 5,383,068 to Shimizu et al., entitled Head Position Recognition Method, A Speed Calculation Method, And A Head Movement Speed Control Device, U.S. Pat. No. 5,392,174 to Suzuki, entitled Method And Apparatus For Controlling The Speed Of Movement Of The Head Of A Disk Drive Apparatus To A Target Track, U.S. Pat. No. 5,434,725 to Hirose et al., entitled Magnetic Disk Driving Device For Controlling The Position Of A Magnetic Head Relative To The Disk, U.S. Pat. No. 5,561,568 to Kisaka, entitled Method And Apparatus For Fast Positioning A Head Of A Recording Device, U.S. Pat. No. 5,608,588 to Kisaka, entitled Method For Controlling Digital Closed Servo Loop System And Disk Storage Apparatus Using The System, U.S. Pat. No. 5,659,438 to Sasamoto et al., entitled Head Positioning Control System Using Stored Voice Coil Motor Correction Data, U.S. Pat. No. 5,739,971 to Yamaki et al., entitled Head-Position Controlling Device, U.S. Pat. No. 5,754,357 to Anderson et al., entitled Method And Apparatus For Moving A Disk Drive Actuator Away From A Magnetic Latch, Japanese Patent No. 59-152562 to Nehira, entitled Magnetic Disk Memory, and Japanese Patent No. 6-52644 to Enozono, entitled Magnetic Disk Device.
The above patents disclose various methods and arrangements for controlling a magnetic disk drive. For example, Anderson et al. '357 discloses a magnetic disk drive control method and arrangement which moves an actuator away from a magnetic latch. Control of the position of the head of a magnetic disk drive is also disclosed (for example,see, Yamaki et al. '971). Kisaka '588 discloses a disk storage apparatus which employs a digital closed servo loop system and a method for controlling that system. Other patents (for example, Suzuki '174) disclose methods and apparatus for controlling the speed of movement of the head of a disk drive.
As mentioned above, each of the above patents is burdened by the disadvantages set forth herein. Moreover, none of the patents discloses or suggests a method and arrangement for controlled head unlatching wherein both an open loop and a closed loop mode of operation are employed, nor do the patents mentioned above disclose changing from the open loop mode of operation to the closed loop mode of operation based on a determination as to whether servo information is accurately detected during performance of an open loop mode of operation.